Fire resistant glass

ABSTRACT

Sheet glass (2) is rendered fire resistant such that it will not shatter under a build-up of heat to 900° C., by providing a thin coating (1) on one or both its surfaces, the coating being stable and adherent to the glass at up to 900° C., the coating preferably comprising an oxide, nitride, oxynitride or fluoride of a metal or of silicon, or a metal silicide, the sheet having been toughened by tempering before or after coating and having its edges (3) ground and polished before the tempering step to remove all imperfections therefrom.

FIELD OF THE INVENTION

This invention relates to fire resistant glass.

DISCUSSION OF THE BACKGROUND

It is important in the design and planning of buildings, particularlyoffices and homes, to give consideration to prevention of the spread offire. There are basically three types of fire resistant glass productwhich are currently used in buildings. Firstly, there is glass which isproduced with a wire mesh or other fire resistant material cast orlaminated into the structure which of course reduces the visibilitythrough the glass. Whilst this type of glass easily breaks whensubjected to heat and flames, the fire resistant material (eg. wiremesh) therein will hold the glass in place to resist spread of fire.This first type of glass product also has the disadvantage of permittingradiation of heat to the area beyond the glass. Secondly, there is clearglass which will not break for at least half-an-hour when subjected tointense heat in a test defined in British Standard BS 476, parts 20, 22and others, i.e. upon build-up of heat to 900° C. This product willprevent the spread of flame but will not stop radiation of heat to thearea beyond the glass. Thirdly, there is glass which will not break forat least half-an-hour when subjected to intense heat (as laid down by BS476), and will also prevent the radiation of intense heat to the areabeyond the glass. This product is currently produced in a series oflaminates of glass and other materials which combine to prevent theconduction of heat.

The third type of glass (the laminated product) is generally expensiveand heavy, and whilst the first type of glass is considerably cheaper,it is not usually aesthetically pleasing. The second type of glass cangive good fire resistance without necessarily being very expensive, andwhilst still being aesthetically pleasing.

There are two fire resistant products currently available which are ofthis second type. The first of these is a sheet of borosilicate glass.Borosilicate glass is of its nature relatively fire resistant. However,it cannot be satisfactorily toughened by tempering and thus does notmeet certain "safety glass" requirements such as those of BritishStandard 6206A. Furthermore, borosilicate glass is more expensive thanordinary silica glass. The second product is a clear ceramic basedproduct which has excellent fire resistance but has very poor opticalquality and is not suitable as a simple replacement for ordinary windowor panel glass.

It would be highly advantageous to be able to provide a fire resistantglass product of the second type described above, made from ordinarysilica based glass since this is relatively inexpensive and it hasexcellent optical properties. However, silica based glass is not ofitself fire resistant: it shatters when exposed to intense heat.Further, toughening the glass by tempering does not significantly affectits fire resistant properties: it still shatters when exposed to intenseheat.

We have now found that a fire resistant product of the second typedescribed above, can be made from silica based glass. Thus, we havedevised a glass for use in buildings particularly where it is deemeddesirable or necessary to prevent the rapid spread of fire and, at thesame time, to give the appearance of a standard piece of "coated" glass.In particular, we have found a way in which such a fire-resistant glasscan be made in a relatively simple and economic way.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, there is provided a fire resistantsheet of glass, which has been toughened by tempering, and which hasdirectly on at least one of its major surfaces a thin coating of acompound which is stable and adherent to the surface at temperatures upto 900° C., such that the coated sheet will not shatter under a build-upof heat to 900° C., the edges of the glass sheet having been ground toremove imperfections before the tempering.

The invention also provides a method of making a fire resistant sheet ofglass which comprises applying to one or both major surfaces of a sheetof glass a thin coating of a compound which is stable and adherent tosaid surface at up to 900° C., the edges of the glass being ground andthe glass being toughened by tempering before or after applying thecoating(s), the resulting coated sheet being such that it will notshatter under a build-up of heat to 900° C.

The invention further provides a fire resistant construction unit foruse in a building, which unit comprises a sheet of glass of theinvention, mounted in a fire resistant steel or timber frame, usingfire-resistant glazing materials, the sheet affording clearuninterrupted vision.

There have been various proposals in the prior art to form coatings onsheet glass. Apart from the well known provision of filters and thelike, it is also known to form metal-containing coatings on a glasssurface. GB-A-1524650 describes tempered glass sheets bearing anelectrically conductive and heat reflective tin oxide film on each sidefor use in oven door window assemblies. The double-coated glass sheethas infra-red reflectance. However, this type of glass is not suitablefor fire-resistant purposes because it will shatter when exposed to abuild-up of heat to 900° C. Heat reflection is not the same as fireresistance: a glass sheet can be highly heat reflective by the presenceof a metal-based heat reflective layer thereon, and yet have little orno fire resistance. GB-A-1565765 describes a method of providing a tinoxide film on glass, by pyrolysing an organic tin compound andsuspending the powder in a gaseous fluorine compound carrier gas. As inGB-A-1524650, the coating gives some protection against heating byreflection of infra-red rays, but the coated glass is not suitable as afire-resistant glass in buildings because under intense heat it willtend to shatter and so permit the spread of fire.

JP-A-57205343 describes the surface treatment of glass to improve itsoptical properties when used in solar batteries, liquid crystals, lasersetc. The glass surfaces are polished with an abrasive material in oil,and then heat-treated and immersed in molten KNO₃ to effect ionexchange. A film of indium oxide can then be applied. This coated glassis very expensive to produce and not suitable for fire resistance inbuildings.

For the purposes of fire resistance, what is required is that a sheet ofglass should remain whole and not fall to pieces when exposed to theintense heat of an adjacent fire. In this way, physical spread of thefire is prevented. We have found that by providing a particular novelcombination of three features in a silica based sheet of glass,excellent fire resistance can be obtained. If one feature of thecombination is omitted, the excellent fire resistance is lost.

Glass sheet in accordance with the present invention affords clearuninterrupted vision since the coating is thin and gives only a smalllevel of visible reflectance. Thus, we have found that a sheet of glasscan be rendered fire resistant without any significant loss of clarityof vision, by the relatively simple process of forming a thintransparent coating as defined above on one or both its surfaces,provided that two very important further requirements are met, namelythat the edges of the glass are ground and that the sheet is toughenedby tempering.

The nature of the glass itself is not critical but we prefer to useordinary glass (i.e. silica based) as produced by the well-knownpatented float line process and conventionally used for both domesticand commercial applications. The thickness of the glass sheet is notcritical. We normally use 6 mm sheet but other thicknesses can be used.The glass is cut using standard techniques and is tempered (toughened),preferably to BS 6206A, in a standard way. In the toughening process,the glass is tempered in a furnace using a cycle time necessary to heatthe glass to a temperature of from 615° C. to 640° C., and then to coolit rapidly. This tempering (toughening) process is well known in itselfand will not be further described herein. It creates a stress patternthrough the product to achieve a break pattern conforming to BS 6206A.British Standard 6206A is a specification for impact performancerequirements for flat safety glass and safety plastics for use inbuildings. Reference should be made to the publication for furtherdetails.

The edges of the glass are ground to ensure that there are noimperfections such as "chips" or "shells". We have found that this is acritically important step, without which the glass will shatter as it isexposed to higher temperatures. It is therefore very important to removeedge imperfections from the sheet glass, and this step is effectedbefore the tempering step.

When glass is to be toughened by tempering, it is known to apply coarsegrinding to the edges just to remove relatively large irregularities.This is called edge "arrissing". The degree of grinding is small and farless than is required in the present invention. It is a preferredfeature of the invention that the ground edges are also thereafterpolished. Conventionally, polishing of glass edges is normally only usedeither to achieve a decorative effect or sometimes to make edges as safeas possible where they will be exposed in the final product. In thepresent invention, grinding can be effected, for example, using adiamond impregnated wheel, and polishing can be effected, for example,using a fibre wheel. Because of the importance of removing all edgeimperfections, the edges should be inspected after treatment to ensurethat they meet the stringent requirements of the invention.

The coatings of the invention can be formed in any convenient way, butwe prefer to use plasma deposition processes such as sputtering, plasmaenhanced chemical vapour deposition, chemical vapour deposition,evaporation or ion beam plasma deposition. Of these, sputtering is oftenthe most convenient. The nature of these processes is well known andfurther description thereof will not therefore be given herein.

The coatings are formed directly on the glass surface. The nature of thecoating can vary widely. We believe that any coating material can beused which is stable to the high temperatures encountered in fireresistance (eg. 900° C.) and which will adhere well to the glass surfaceunder these conditions and in ordinary use. Among the preferred coatingmaterials are oxides, nitrides, oxynitrides and fluorides of silicon ora metal, and metal silicides (including any mixture of two or more suchmaterials). The particular choice of coating material will depend oncircumstances such as cost and the application technique to be used. Weprefer to use tin oxide and to apply it by sputtering, but there aremany other possibilities including oxides or other compounds ofaluminium, nickel, chromium, titanium, copper and alloys such asnickel-chromium alloys and stainless steel.

The thickness of the coating is preferably controlled to be the minimumrequired to give the desired fire resistance. This is advantageous botheconomically and also in that the thinner the coating, the lessinterference there is in visibility through the glass. Generally, thecoating thickness will be in the range from 10 angstroms to 1 micron,with coatings usually in the lower end of this range. The reduction invisible light transmission due to the coating will normally be less than10%. For tin oxide, the preferred minimum thickness is about 10angstroms. It will be understood that the measurement of very thin metaloxide coatings is inherently imprecise and we intend to indicate theorder of magnitude rather than any precise figure. The optimum thicknessin any particular case can be determined by routine trial andexperiment. We believe that the minimum thickness required to achievethe desired fire resistance is much the same for all the coatings whichcan be used.

In the method of the invention, the coating can be applied to the glassbefore or after the tempering step. However, the edge treatment must beeffected before the tempering. Thus, for example, sheets of glass can beedged and tempered, and then coated or, alternatively, coated glass canbe edged and then tempered.

The glass sheets of the invention can be coated on one side only, andprovided this side is the one exposed to the fire, fire resistance willbe obtained. However, it is usually much more convenient to coat bothsides of the glass so that there are no restrictions of orientation inits final use.

The glass sheets of the invention are primarily intended for use inbuilding construction to provide requisite fire resistance properties.Thus, they can be used for external or internal windows, for example, orin internal walls and screens, or other glazed units. Normally, theywill be mounted in a fire resistant frame of metal or wood, usingappropriate fire resisting glazing materials such as tapes and the like,so that the unit as a whole provides the desired fire resistance.

In order that the invention may be more fully understood, the followingExamples are given by way of illustration only. In the Examples,reference is made to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of furnace temperature during testing of glass,against time;

FIG. 2 is a section through one embodiment of sheet of fire resistantglass of the invention; and

FIG. 3 is a plan view of an embodiment of construction unit of theinvention, given by way of example only.

EXAMPLE 1

A 6 mm sheet of glass approximately 1 m square was edge ground andpolished to remove any edge imperfections. The sheet was then temperedin a conventional tempering oven and quenched to achieve a break patternconforming to BS 6206A. The toughened sheet was then coated on bothfaces with a thin coating of tin oxide using a vacuum DC magnetronsputtering plant. The sheet was first coated on one side, and thenpassed through the plant a second time to coat the other side. Thecoating thickness was about 10 angstroms.

The coated glass had the ability to withstand a build-up in heat to atleast 900° C. as required by BS 476, without the coating burning off.(British Standard 476 relates to fire tests on building materials andstructures and parts 20 and 22 thereof relate to methods fordetermination of the fire resistance of non-loadbearing elements ofconstruction. Reference should be made to this publication of theBritish Standards Institution for further details.) The accompanyingFIG. 1 shows the furnace temperature (the glass temperature will bevirtually the same) during testing of the glass. The coating remainedintact.

The accompanying FIG. 2 shows in section (but not to scale) the coatedglass sheet of the Example. The thin tin oxide coatings 1 are present onthe two faces of the sheet 2. The ground and polished edges 3 of thesheet are also shown. FIG. 3 shows a construction unit of the inventioncomprising a rigid rectangular steel or timber fire resistant frame 10in which is mounted a sheet 11 of fire resistant glass of the invention.The glazing materials (12) are also fire resistant. The unit can ofcourse be single or double glazed.

EXAMPLE 2

When the preparation of Example 1 is repeated, but with the omission ofthe edge polishing step so that there has only been a rough removal ofsharp edges by coarse grinding, the resulting coated glass sheet doesnot have satisfactory fire resistance. The sheet shatters upon exposureto the heat as the temperature rises.

EXAMPLE 3

When the preparation of Example 1 is repeated using other oxides, andalso nitrides, oxynitrides and fluorides of various metals and ofsilicon, the results obtained are similar to those of Example 1. In thecase of sputtering silicon, a low frequency magnetron is used. The useof a coating of silicides is also very satisfactory.

EXAMPLE 4

A construction unit as described with reference to FIG. 3 herein wasmade up 3 m square and tested for fire resistance. The unit remainedintact for over 30 minutes even at temperatures over 900° C.

What is claimed is:
 1. A fire resistant coated sheet of glass, which hasbeen toughened by tempering, comprising a glass sheet which has applieddirectly on at least one major surface of said sheet a coating of acompound which is stable and adherent to the surface at temperatures upto 900° C., such that the coated sheet will not shatter under a build-upof heat of 900° C., the edges of the glass sheet having been ground andpolished to remove imperfections before tempering.
 2. A coated sheet ofglass according to claim 1, wherein the coating is an oxide, nitride,oxynitride or fluoride of a metal or silicon, a metal silicide.
 3. Acoated sheet of glass according to claim 2, wherein the coating is ametallic oxide selected from the group consisting of tin oxide, titaniumoxide and chromium oxide.
 4. A coated sheet of glass according to claim1, 2 or 3, wherein said sheet has two major surfaces, and both majorsurfaces have said coating thereon.
 5. A coated sheet of glass accordingto any of claims 1 to 3, wherein said sheet is made of silica glasswhich has been tempered by heating to 615° C. to 640° C. and thenrapidly cooled.
 6. The coated sheet as claimed in claim 1, wherein thethickness of the coating is from 10 angstroms to 1 micron.
 7. A sheet ofsilica glass of thickness 4 to 8 mm which has been tempered to toughenit by heating to 615° C. to 640° C. and then cooled, wherein the glassmeets the breakage requirements of BS 6206A, the edges of the sheethaving been ground and polished to remove imperfections beforetempering, and wherein each major face of the sheet has a coating of tinoxide sputter coated directly thereon such that the sheet will notshatter under a build-up of heat to 900° C., the sheet affording clearuninterrupted vision.
 8. The sheet as claimed in claim 7, wherein thethickness of the coating is from 10 angstroms to 1 micron.
 9. A methodof making a fire resistant coated sheet of glass which comprisesapplying to one or both major surfaces of a sheet of glass a coating ofa compound which is stable and adherent to said surface at up to 900° C.the edges of the glass being ground and polished and the glass beingtoughened by tempering before or after applying the coating(s), theresulting coated sheet being such that it will not shatter under abuild-up of heat to 900° C.
 10. A method according to claim 9, whereinthe coating is effected by plasma deposition and said coating is anoxide, nitride, oxynitride or fluoride of a metal, silicon, or a metalsilicide.
 11. A method according to claim 9 or 10, wherein a metallicoxide coating is formed by sputter deposition.
 12. The method as claimedin claim 9, wherein the thickness of the coating is from 10 angstroms to1 micron.
 13. A fire resistant construction unit for use in a building,which unit comprises a sheet of glass as claimed in any of claims 1, 2,3 or 6, mounted in a fire resistant steel or timber frame, using fireresistant glazing materials, the sheet affording clear uninterruptedvision.